Brake actuating apparatus using an electric motor

ABSTRACT

A brake actuating apparatus includes a caliper body with a cylinder. An electric motor is fixed to the caliper body. A pressing piston is installed in the cylinder. A rotational shaft is installed at the center of the housing to be rotated by the motor. A head is attached to the rotational shaft and defines a fluid-receiving space in cooperation with the housing. The rotation of head varies the volume of space, thereby moving the pressing piston.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. application Ser.No. 11/529,153 filed Sep. 28, 2006, now abandoned, which is acontinuation application under 35 U.S.C. §365(c) of InternationalApplication No. PCT/KR2005/000904, filed Mar. 28, 2005 designating theUnited States. International Application No. PCT/KR2005/000904 waspublished in English as WO2005/092685 A1 on Oct. 6, 2005. Thisapplication further claims the benefit of the earlier filing dates under35 U.S.C. §365(b) of Korean Patent Application No. 10-2004-0021218 filedMar. 29, 2004. This application incorporates herein by reference U.S.application Ser. No. 11/529,123, International Application No.PCT/KR2005/000904 including International Publication No. WO2005/092685A1 and Korean Patent Application No. 10-2004-0021218 in their entirety.

BACKGROUND

1. Field

The present disclosure relates to a brake actuating apparatus, and moreparticularly, to a brake actuating apparatus using an electric motor.

2. Discussion on Related Technology

A typical hydraulic braking apparatus comprises a hydraulic circuit,wherein pedal pressure generated through depression of a pedal by adriver is increased in a master cylinder and a booster and thentransmitted through hydraulic tubing to a braking apparatus mounted toeach of road wheels. The hydraulic brake has disadvantages in that it isimpossible to perform braking if the hydraulic tubing is damaged, ittakes a great deal of time to transmit a pedal operation signal forbraking to the brake through the hydraulic tubing, resulting in poorresponsiveness, and a plurality of parts including the hydraulic tubingare required, resulting in the increased weight of a vehicle.

Recently, there has been proposed a braking apparatus, wherein insteadof such a complicated hydraulic circuit, a motion converting means suchas a ball screw is used for converting a rotational motion from a motorto a linear motion so as to urge a brake pad, thereby performing thebraking function. Such a type of braking apparatus is called“brake-by-wire” type and has an advantage of easy control. As for the“brake-by-wire” type braking apparatus, however, a relativelylarge-sized motor, a reducer and a means for converting a rotationalforce of the motor into a liner motion are inevitably required in orderto obtain an appropriate braking force. Moreover, the braking apparatusmay further have a clutch used for controlling transmission andinterruption of the power from the motor in order to improve theresponsiveness of the brake, which causes disadvantages of increase inthe volume of the apparatus, difficulty in manufacturing the apparatus,and increased costs. Particularly, the apparatus has a drawback in thatmechanical braking cannot be performed if an unexpected electricalfailure or defect is produced in the apparatus.

As a braking apparatus for solving the problems in the hydraulic brakingapparatus and the “brake-by-wire” type braking apparatus, there has beenproposed an apparatus that employs a hybrid braking system using both amotor and hydraulic pressure. U.S. Pat. No. 5,348,123 entitled “BrakeActuating Apparatus for a Vehicle” discloses the technical constitutionof a braking apparatus that controls the pressure of a fluid in acylinder for urging a brake pad, using a motor. As shown in FIG. 16, thepatent discloses a brake system in which a rotational motion from amotor 3 is converted into a linear motion by means of a ball screw 5 andthen transmitted to a driving piston 7 and the advance of the drivingpiston 7 causes a working fluid 1 to urge a pressing piston 9 so thatthe pressing piston can be moved forward, thereby performing braking.

However, the brake actuating apparatus disclosed in the U.S. Patentshould inevitably have a motion converting means such as a ball screw inorder to convert the rotational motion from the motor to the linearmotion. Further, the brake actuating apparatus should be additionallyprovided with a structure for securely returning the member, which hasbeen moved forward through the conversion of the rotational motion intothe linear motion by the motion converting means, after braking.Accordingly, there are disadvantages in that the structure of theapparatus is complicated, it is difficult to manufacture and assemblethe apparatus, and production costs increase.

The discussion in this section is to provide general backgroundinformation, and does not constitute an admission of prior art.

SUMMARY OF CERTAIN INVENTIVE ASPECTS

An aspect of the invention provides a brake actuating apparatus, whichmay comprise: a caliper body comprising a cylinder, which comprises afirst end and a second end; a piston movably engaged with the cylinderat the first end, wherein at least one of the piston and the caliperbody is configured to hold a brake pad; a shaft rotatable about an axis;a plug engaged with the cylinder at the second end, the plug comprisinga head receiver; and a head connected to the shaft at a distance fromthe axis, the head being rotatable about the axis and movable relativeto the plug as the shaft rotates about the axis, the head being receivedby and movably engaged with the head receiver; wherein the cylinder, thepiston and the plug in combination define a first space having a firstvolume, which is variable depending upon a position of the pistonrelative to the plug; wherein the head receiver in combination with thehead defines a second space having a second volume, which is variabledepending upon the position of the head relative to the plug, the secondspace being in fluid communication with the first space; wherein the sumof the first volume and the second volume is substantially constant.

In the foregoing apparatus, the head receiver may comprise a grooveformed in the plug. The groove may be configured to guide rotationalmovement of the head about the axis. At least part of the head may beslidably engaged within the groove. The groove may have an openingfacing the first space. The head receiver may further comprise a holeextending circumferentially about the axis from the groove, and whereinthe head comprises a rod engaged with the hole and slidable relative tothe hole. The rod may have a cross-sectional shape selected from thegroup consisting of circle, oval and polygon. The apparatus may furthercomprise a sealing ring surrounding the rod. The head receiver maycomprise one or more additional grooves, wherein the groove and the oneor more additional grooves are disposed in the plug with thesubstantially same angular interval between two immediately neighboringgrooves.

Still in the foregoing apparatus, the apparatus may further comprise aconnector connecting between the shaft and head. At least part of theconnector may be located within the first space. At least part of theconnector may be located between the plug and the piston. The secondspace may be defined by one or more walls formed in the plug, andwherein the plug may further comprise a passage interconnecting thefirst and second spaces, the passage enabling the fluid communicationbetween the first and second spaces. At least part of the plug may belocated between the head and the piston.

Further in the foregoing apparatus, he plug may comprise a firstcircular disk having a first radius and a second disk having a secondradius, wherein the first and second circular disks may be integratedwith each other, wherein the first disk may face the first space, andwherein the first radius may be smaller than the second radius. The plugmay comprise a through hole extending along the axis and the shaftpasses through the through hole. The apparatus may further comprise anelectric motor attached to the caliper body and configured to rotate theshaft. The head may be movable between a first position and a secondposition, wherein the head may be configured to rotate in a firstrotational direction, stop at a third position and rotate in a secondrotational direction which is opposite to the first rotationaldirection, and wherein the third position may be located between thefirst position and the second position.

Another aspect of the invention provides an automobile, which maycomprise: the foregoing apparatus, wherein the first and second spacesare filled with a brake fluid; and a brake pad attached to the at leastone of the piston and the caliper body. The automobile may comprise oneselected from the group consisting of passenger car, truck, bus, golfcart and motor cycle.

Still another aspect of the invention provides a method of actuating abrake, which may comprise: providing the foregoing apparatus; rotatingthe shaft in a first direction so as to rotate the head about the axisand to move relative to the plug, whereby the second volume decreases,at least part of the fluid moves from the second space to the firstspace, and the piston moves relative to the caliper body. The method mayfurther comprise rotating the shaft in a second direction opposite tothe first direction so as to rotate the head about the axis and moverelative to the plug, whereby the second volume increases, at least partof the fluid moves from the first space to the second space, and thepiston moves relative to the caliper body.

An aspect of the present invention is to provide a brake actuatingapparatus that uses both an electric motor and a fluid and converts arotational motion from the motor into a force for pressurizing the fluidso that a frictional member such as a brake pad can be pressed against abrake disk, thereby performing a braking function, without a means forconverting the rotational motion from the motor into a linear motion.

Another aspect of the present invention is to provide a brake actuatingapparatus that further comprises a means for mechanically pressing thefrictional member such as a brake pad against the brake disk to performthe braking function if the electric motor is out of order.

A brake actuating apparatus according to an aspect of the presentinvention comprises a caliper body with a cylinder; a motor fixed to thecaliper body; a pressing piston installed in the cylinder to moveforward and rearward, for pressing a brake pad disposed to be broughtinto frictional contact with a frictional surface of a brake disk whenthe pressing piston moves forward; a disk-shaped housing that is spacedapart by a predetermined distance rearward from the pressing piston andfixedly installed at the cylinder to maintain airtightness between aninner periphery of the cylinder and the housing and has at least oneopening formed therein to be directed toward a space between thepressing piston and the housing; a rotational shaft installed in thehousing to rotate by receiving a rotational force transmitted from themotor; a power transmission means for transmitting the rotational forceof the motor to the rotational shaft; and a fluid-pressurizing memberthat is installed in the housing and has a first end fixed to therotational shaft and a second end with a portion thereof received in theopening of the housing so as to define a closed fluid-receiving space bythe pressing piston, the housing and the portion of the second endreceived in the opening. The fluid-pressurizing member enters the closedfluid-receiving space to increase pressure in the fluid-receiving spaceso that the pressing piston is urged if the rotational shaft is rotatedin one direction, and the fluid-pressurizing member is retracted fromthe closed fluid-receiving space into the housing if the rotationalshaft is rotated in an opposite direction.

The opening of the housing may comprise a guide groove formed to have apredetermined radius of curvature, width and central angle around therotational shaft and to face the fluid-receiving space, a first passageextending by a predetermined length from a circumferential end of theguide groove into the housing with the same radius of curvature as theguide groove and a predetermined sectional shape, and a second passagecommunicating with the first passage and extending to a rear surface ofthe housing. The second end of the fluid-pressurizing member, whichdefines the fluid-receiving space in cooperation with the housing andgenerates pressure transmitted to the pressing piston, may have thesubstantially same radius of curvature and sectional shape as the firstpassage, and a portion of the second end may be located in the guidegroove and another portion of the second end may be received in thefirst passage to be moved into and withdrawn from the fluid-receivingspace by means of rotation of the rotational shaft.

In an embodiment of the present invention, when the fluid-pressurizingmember fixed to the rotational shaft receives the rotational force ofthe motor and the second end of the fluid-pressurizing member enters thefluid-receiving space along the guide groove of the housing, the volumeof the fluid-receiving space decreases and the pressure of the workingfluid received in the fluid-receiving space increases. The increasedpressure of the working fluid is applied to an inner surface of thepressing piston, so that the pressing piston is advanced to urge a brakepad. The urged brake pad is brought into contact with a frictionalsurface of a brake disk, thereby performing a braking function. Thebrake actuating apparatus according to an embodiment of the presentinvention does not have a means for converting the rotational motionfrom the motor into a linear motion for urging the pressing piston. Thatis, the fluid-pressurizing member is connected to and rotated with therotational shaft. Further, in an embodiment of the present invention,the sectional area of the fluid-pressurizing member defining thefluid-receiving space is smaller than that of the pressing piston. Alarge force can be applied to the pressing piston to perform the brakingfunction even though the fluid-pressurizing member is rotated with asmall force, according to the Pascal's theory regarding a fluid. Thatis, the sectional area of the second end of the fluid-pressurizingmember in a rotating direction, which enters the fluid receiving space,is significantly smaller than the sectional area of the pressing pistonin a moving direction. Accordingly, when the fluid-pressurizing memberis caused to enter the fluid-receiving space with a small force,pressure produced in the fluid-receiving space is applied to thepressing piston with a larger sectional area according to the Pascal'stheory, so that the brake pad is urged with a large force.

In an embodiment of the present invention, the guide groove of theopening formed in the housing may be formed in a front surface of thehousing directed toward the pressing piston, or a small diameter portionprotruding toward the pressing piston may be formed in the housing andthe guide groove may be formed in a side surface of the small diameterportion directed toward the inner periphery of the cylinder.

If the guide groove is formed in the front surface of the housingdirected toward the pressing piston, the second end of thefluid-pressurizing member may be inserted into and placed in the firstpassage through the guide groove, or the second end of thefluid-pressurizing member may be inserted into and placed in the firstpassage through the second passage. Preferably, the housing comprises afirst disk formed with the guide groove and the first passage and asecond disk formed with the second passage communicating with the firstpassage, a radially outer wall of the first disk at which the guidegroove will be formed, and a surface of the first disk which is directedtoward the second disk and at which the first passage will be formed arepartially removed, the fluid-pressurizing member is provided between thefirst disk and the second disk, the first end of the fluid-pressurizingmember is fixed to the rotational shaft, and the second end thereof hasa stepped arcuate projection formed to be inserted into the firstpassage. In this case, the guide groove and the first passage aredefined by the inner periphery of the cylinder and the first and seconddisks.

If a small diameter portion protruding toward the pressing piston isformed in the housing and the guide groove is formed in a side surfaceof the small diameter portion directed toward the inner periphery of thecylinder, the housing preferably comprises a first disk provided with alarge diameter portion and a small diameter portion, and a second diskformed with the second passage. The first disk has the large diameterportion and the small diameter portion protruding toward the pressingpiston, and is formed with a guide groove in a side surface of the smalldiameter portion directed toward the inner periphery of the cylinder anda first passage extending circumferentially from the guide groove. Thesecond disk is formed with a through-hole communicating with the firstpassage. Further, a radially inner wall of the first disk at which theguide groove and the first passage will be formed and a surface of thefirst disk directed toward the second disk are removed, thefluid-pressurizing member is installed between the first and seconddisks and disposed such that the second end can be inserted into thefirst passage to rotate through a certain angle. In this case, the guidegroove and the first passage are defined by the first disk, the seconddisk and the fluid-pressurizing member. For the purpose of easiness ofmanufacture, it is preferred that circumferential sidewalls for definingthe first passage be removed in the small diameter portion of the firstdisk and an additional sidewall ring be inserted between the smalldiameter portion of the first disk and the fluid-pressurizing member toform sidewalls of the first passage. The sidewall ring takes the shapeof a ring with a predetermined width and has a through-hole formed at aposition corresponding to the guide groove formed in the small diameterportion. The sidewall ring also has sidewalls formed on an innerperiphery thereof at positions corresponding to the removedcircumferential sidewalls for defining the first passage.

Moreover, in order to transmit a larger braking force, a plurality ofguide grooves and first passages may be formed at a predeterminedinterval on a circle with a radius of curvature in the housing, and aplurality of fluid-pressurizing members may be fixed to the rotationalshaft at the same interval as the guide grooves. The moving distance ofthe pressing piston for urging the disk pad is obtained by dividing thevolume of the fluid-pressurizing members inserted into thefluid-receiving space by the sectional area of the pressuring piston.Accordingly, the stroke of the pressing piston can be appropriatelyadjusted by properly selecting the number, length and sectional area ofthe fluid-pressurizing members moved into the fluid-receiving space bymeans of rotation.

Furthermore, in the brake actuating apparatus according to an embodimentof the present invention, to supplement the working fluid upon leakthereof due to operation for a long time, an oil-supplying holecommunicating with an outer periphery of the housing is formed in aradially outer side surface of the guide groove of the housing, and thebrake actuating apparatus further comprises an oil-supplying tank thathas an oil-supplying port communicating with the oil supplying hole, anda working fluid contained therein.

To mechanically rotate the rotational shaft if the motor is out oforder, it is more desirable that the brake actuating apparatus accordingto an embodiment of the present invention further comprise a lever forrotating the rotational shaft only in a direction in which thefluid-pressurizing member enters the fluid-receiving space.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a brake actuating apparatus according toan embodiment of the present invention.

FIG. 2 is a perspective view of an embodiment of a housing and afluid-pressurizing member of the brake actuating apparatus shown in FIG.1, with the housing and the fluid-pressurizing member separated fromeach other.

FIG. 3 is a schematic view of a brake actuating apparatus according toanother embodiment of the present invention.

FIG. 4 is a perspective view of an embodiment of a housing and afluid-pressurizing member of the brake actuating apparatus shown in FIG.3, with the housing and the fluid-pressurizing member separated fromeach other.

FIG. 5 is a plan view of the housing shown in FIG. 4.

FIGS. 6 (a) and (b) are sectional views of the housing taken along lineA-A and line B-B in FIG. 5, respectively.

FIG. 7 is a perspective view of another embodiment of the housing andthe fluid-pressurizing member in the brake actuating apparatus accordingto an embodiment of the present invention, with the housing and thefluid-pressurizing member separated from each other.

FIGS. 8 (a) and (b) are sectional views of the housing taken along lineC-C and line D-D in FIG. 7, respectively.

FIG. 9 is a perspective view of another embodiment of the housing andthe fluid-pressurizing member shown in FIG. 2, with the housing and thefluid-pressurizing member separated from each other.

FIG. 10 is a perspective view of another embodiment of the housing andthe fluid-pressurizing member shown in FIG. 7, with the housing and thefluid-pressurizing member separated from each other.

FIG. 11 is a perspective view of a further embodiment of the housing andthe fluid-pressurizing member in the brake actuating apparatus accordingto an embodiment of the present invention, with the housing and thefluid-pressurizing member separated from each other.

FIG. 12 is a perspective view of a still further embodiment of thehousing and the fluid-pressurizing member in an electric brakingapparatus according to an embodiment of the present invention, with thehousing and the fluid-pressurizing member separated from each other.

FIG. 13 is a schematic view of a brake actuating apparatus according toa further embodiment of the present invention.

FIG. 14 is a perspective view of an embodiment of a housing and afluid-pressurizing member of the brake actuating apparatus shown in FIG.13, with the housing and the fluid-pressurizing member separated fromeach other.

FIG. 15 is a sectional view taken along line E-E in FIG. 14, showing astate where the housing and the fluid-pressurizing member are assembled.

FIG. 16 is a schematic view of an exemplary brake actuating apparatusfor a vehicle.

FIG. 17 is a perspective view of a modified version of the embodiment ofFIG. 4.

FIGS. 18A, 18B and 18C are reproduction of FIG. 5, illustrating threedifferent positions of a fluid-pressurizing member relative to a guidegroove.

FIGS. 19A, 19B and 19C show polygonal, oval and circular sections of afluid-pressurizing member, respectively.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, various embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings.

FIG. 1 is a schematic view of a brake actuating apparatus according toan embodiment of the present invention, and FIG. 2 is a perspective viewof an embodiment of a housing and a fluid-pressurizing member of thebrake actuating apparatus shown in FIG. 1, with the housing and thefluid-pressurizing member separated from each other.

As shown in FIG. 1, the brake actuating apparatus of this embodimentcomprises a caliper body 80 with a cylinder 85, an electric motor 45fixed to the caliper body 80, a pressing piston 70 installed within thecylinder 85, a housing or plug 62 that is spaced apart rearward by apredetermined distance from the pressing piston 70 and installed fixedlyat the cylinder 85 to maintain airtightness with an inner periphery ofthe cylinder 85, a rotational shaft 61 installed at the center of thehousing 62 to be rotated by receiving a rotational force transmittedfrom the motor 45, and a power transmission means 50 for transmittingthe rotational force of the motor 45 to the rotational shaft 61.

Referring to FIG. 2, the housing 62 takes the shape of a disk and isformed with at least one opening or head receiver directed toward aspace between the housing and the pressing piston 70. The openingcomprises a guide groove 62 a formed in a front surface of the housingdirected toward the pressing piston 70, a first passage 62 b extendingby a predetermined length at a circumferential end of the guide groove62 a into the housing 62, and a second passage 62 g extending at a rearside of the first passage 62 b to communicate with a rear surface of thehousing 62. Further, the brake actuating apparatus of this embodimentcomprises a fluid-pressurizing member or head 63 fixed to the rotationalshaft 61 to define a fluid-receiving space 72 hermetically closed by thepressing piston 70, the inner periphery of the cylinder 85 and thehousing 62. The fluid-pressurizing member 63 is installed such that itcan be moved into and retreated from the inside of the fluid-receivingspace 72. Referring to FIG. 2, as for the fluid-pressurizing member 63in this embodiment, a first end 63 a thereof is fixed to the rotationalshaft 61 and a portion of a second end or rod 63 b is inserted into thefirst passage 62 b through the guide groove 62 a of the housing 62. Thefirst and second ends 63 a and 63 b are connected to each other via anintermediate portion 63 c. Accordingly, the closed fluid-receiving space72 is defined by the inner periphery of the cylinder 85, the pressingpiston 70, the housing 62 and the second end 63 h of thefluid-pressurizing member 63 inserted into the first passage 62 b.

In this embodiment, the caliper body 80 is, but not limited to, afloating type caliper that supports brake pads such that the brake padscan be moved in an axial direction of a brake disk 99 upon braking.Brake pads 90 are installed to face both frictional surfaces of thebrake disk 99. When the pressure of a working fluid in thefluid-receiving space 72 increases, the pressing piston 70 advancesrightward in FIG. 1 to urge the brake pads 90. Linings 91 of the pair ofthe brake pads 90 are disposed to come into contact with the frictionalsurfaces of the brake disk 99. A sealing O-ring 71 is mounted on anouter periphery of the pressing piston 70. Reference numeral 73designates a seal ring for preventing dust and the like from intrudinginto a clearance between the cylinder of the caliper body 80 and thepressing piston 70.

The housing 62 is spaced apart by the predetermined distance rearwardfrom the pressing piston 70 and fixedly installed at that position todefine the closed fluid-receiving space 72 between the housing 62 andthe pressing piston 70. Although the housing 62 in this embodiment has acylindrical shape and is fixedly installed on the inner periphery of thecylinder 85, it is not limited thereto. The housing may be installed atthe rear of the cylinder to define the closed fluid-receiving space 72between the pressing piston 70 and the housing. A sealing O-ring 64 isprovided between an outer periphery of the housing 62 and the innerperiphery of the cylinder 85. Referring to FIG. 2, the housing 62 inthis embodiment has the guide groove 62 a formed in the front surfacethereof directed toward the pressing piston 70. The guide groove 62 atakes the shape of an arc with a predetermined radius of curvature,width and central angle. Further, the first passage 62 b is formed atthe circumferential end of the guide groove 62 a of the housing 62 toextend into the housing 62 by the predetermined length. The firstpassage 62 b has the same radius of curvature as the guide groove 62 a,and a predetermined shape in cross section. Moreover, the second passage62 g is formed in the housing 62 to extend from the rear side of thefirst passage 62 b and to communicate with the rear surface of thehousing 62. The second passage 62 g functions to cause air to be suckedor exhausted therethrough, thereby ensuring smooth movement of themovable member 63. The guide groove 62 a, the first passage 62 b and thesecond passage 62 g constitute the opening of the housing 62. Referencenumeral 62 d that has not been explained designates a shaft supportinghole for use in receiving and supporting the rotational shaft 61.

Referring to FIG. 2, the fluid-pressurizing member 63 of the illustratedembodiment comprises the first end 63 a fixed to the rotational shaft 61and radially extending by a predetermined length, the intermediateportion 63 c axially extending from the first end by a predeterminedlength, and the second end 63 b circumferentially extending from theintermediate portion 63 c to have a radius of curvature that issubstantially identical with that of the guide groove 62 a and the firstpassage 62 b. The second end 63 b of the fluid-pressurizing member 63 isa free end and has a radius of curvature and a sectional shape that aresubstantially identical with those of the first passage 62 b. When thefluid-pressurizing member is installed, a portion of the second end 63 bis placed in the guide groove 62 a and another portion thereof isinserted into and received in the first passage 62 b. That is, thesecond end 63 b of the movable member 63 inserted into the first passage62 b is adapted to rotate in the first passage 62 b while being guidedby the guide groove 62 a upon rotation of the rotational shaft 61.Further, the first passage 62 b and the second end 63 b of the movablemember 63 have the substantially same shape in cross section and can beslid relative to each other in a contact state, so that if the movablemember 63 is moved in the first passage 62 b, the working fluid in thefluid-receiving space 72 can be prevented from leaking into the secondpassage 62 g through the first passage 62 b. Although not shown, asealing member may be further installed to prevent the working fluidfrom leaking through a clearance between the second end 63 b of themovable member 63 and the first passage 62 b, if necessary.

The rotational shaft 61 is installed at the center of the housing 62 tobe rotated through certain angles by receiving the rotational forcetransmitted from the motor 45. When the rotational shaft 61 is rotatedin one direction, the second end 63 b of the fluid-pressurizing member63 that has been moveably inserted into the first passage 62 b entersinto the fluid-receiving space 72 from the inside of the housing 62 toincrease the pressure of the working fluid, thereby causing the pressingpiston 70 to advance. When the rotational shaft 61 is rotated in anopposite direction, the second end 63 b of the fluid-pressurizing member63 is moved from the fluid-receiving space 72 and then received withinthe housing 62 to decrease the pressure of the working fluid, therebycausing the pressing piston 70 to retract. Contrary to the brakeactuating apparatus shown in FIG. 16, in the brake actuating apparatusof this embodiment comprising the rotational shaft 61, the housing 62and the fluid-pressurizing member 63, the rotational force istransmitted to the fluid-pressurizing member 63 that in turn directlypressurizes the working fluid without converting a rotational motionfrom the motor into a linear motion. Thus, the pressing piston 70 isadvanced to perform a braking function. Moreover, contrary to ahydraulic brake actuating apparatus, the pressing piston 70 can beadvanced using the motor without additional supply of an externalworking fluid into the fluid-receiving space 72 in the cylinder so as toperform the braking function.

Referring to FIG. 1, the motor 45 can rotate in forward and reversedirections and is fixed to the caliper body 80. In this embodiment, thepower transmission means 50 comprises a first gear 51 coupled to a shaftof the motor and a second gear 52 engaged with the first gear 51 andfixed to the rotational shaft 61. The power transmission means 50adjusts the rotational force of the motor to obtain a proper speed andtorque and transmits it to the rotational shaft 61 of a movable means60. Accordingly, the power transmission means is not limited to theillustrated embodiment, but can be modified to any other configurationsby using a reducer such as an appropriate number of gears or a harmonicdrive. Although not shown, the brake actuating apparatus for a vehicleaccording to this embodiment may also further have an additional meansfor returning the fluid-pressurizing member 63 to its initial position,which is a position thereof prior to braking, after the pressing piston70 has advanced to perform the braking function. That is, when therotational force of the motor 45 is not transmitted to the rotationalshaft 61, a returning spring may be provided between the movable memberand the guide groove so as to return the movable member to its initialposition.

Next, the operation of this embodiment will be briefly described withreference to FIG. 1. Once a driver of a vehicle depresses a brake pedalfor braking the vehicle, a pressure sensor 20 detects pressure appliedto the brake pedal and transmits a signal corresponding to the detectionto an electronic control unit 40. The electronic control unit 40transmits a motor control signal to the motor 45 so as to controlbraking of each road wheel, in response to a signal transmitted from anadditional driving condition sensor 30 for detecting the speed of thevehicle and the like and the signal transmitted from the pressure sensor20. When the motor 45 is rotated in response to the motor controlsignal, the rotational force of the motor 45 is transmitted to therotational shaft 61 through the first and second gears 51 and 52 of thepower transmission means 50. Upon rotation of the rotational shaft 61,the movable member 63 fixed to the rotational shaft 61 is rotated sothat the second end 63 b of the movable member is withdrawn from thefirst passage 62 b of the housing 62 and pushes the working fluidreceived in the guide groove 62 a. As the volume of the fluid-receivingspace 72 is decreased, the pressure of the working fluid increases andthe pressing piston 70 is advanced rightward in the figure due to theincreased pressure of the working fluid, thereby performing braking. Atthis time, the sectional area of the pressing piston 70 is greatlylarger than that of the second end 63 b of the fluid-pressurizing member63. Therefore, the second end 63 b of the fluid-pressurizing member 63is introduced into the fluid-receiving space 72 with a small forceaccording to the Pascal's theory. The increased pressure of the workingfluid is applied to the pressing piston 70 with a larger sectional area,so that the brake pads 90 can be urged with a large force. According tothe Pascal's theory, the braking force can be boosted, and thus, it ispossible to make the motor compact.

FIG. 3 is a schematic view of a brake actuating apparatus according toanother embodiment of the present invention, FIG. 4 is a perspectiveview of an embodiment of a housing and a fluid-pressurizing member ofthe brake actuating apparatus shown in FIG. 3, with the housing and thefluid-pressurizing member separated from each other, FIG. 5 is a planview of the housing shown in FIG. 4, and FIGS. 6 (a) and (b) aresectional views of the housing taken along line A-A and line B-B in FIG.5, respectively.

The brake actuating apparatus for a vehicle according to an embodimentshown in FIG. 3 is different from an embodiment shown in FIG. 1 in thata plurality of fluid-pressurizing members 63 are provided as shown inFIG. 4 and the brake actuating apparatus has a structure forreplenishing a fluid-receiving space 72 with a working fluid if theworking fluid leaks from the fluid-receiving space when the apparatus isoperated for a long time. The brake actuating apparatus includes anelectric motor 45 shown in FIG. 3. Referring to FIG. 17, in oneembodiment, a sealing ring 630 surrounds the pressurizing member 63.Referring to FIGS. 19A, 19B and 19C, the section of the pressurizingmember 63 can have a shape of polygon, oval or circle.

Referring to FIGS. 4 and 5, a housing 62 in this embodiment isequiangularly formed with four guide grooves 62 a on the same circle ina front surface thereof directed toward a pressing piston 70. Theplurality of guide grooves 62 a take the shapes of circular arcs withthe same width and central angle. Further, each of the guide grooves 62a has a first passage 62 b extending by a predetermined length from acircumferential end thereof into the housing 62. The first passage 62 bhas the same radius of curvature as the guide groove 62 a and apredetermined shape in cross section. Moreover, a second passage 62 gextends at the rear side of the first passage 62 b to communicate withthe rear surface of the housing 62.

In this embodiment, the apparatus has fluid-pressurizing members 63 ofwhich the number is identical with that of the guide grooves 62 a andfirst ends 63 a are equiangularly fixed at positions corresponding tothe guide grooves 62 a to a fixing disk 66 that is fixed to an end ofthe rotational shaft 61 to face the surface of the housing 62 where theguide grooves 62 a are formed. That is, the fluid-pressurizing members63 are fixedly disposed on the surface of the fixing disk 66, which isdirected toward the guide grooves 62 a, at the same interval as theguide grooves 62 a. The first end 63 a of each of the fluid-pressurizingmembers 63 is fixed to the fixing disk 66 and axially extends by apredetermined distance, and a second end or rod 63 b thereofcircumferentially extends from the first end 63 a to have a radius ofcurvature that is substantially identical with that of the guide groove62 a and the first passage 62 b. The second end 63 b of each of thefluid-pressurizing members 63 is a free end and has a sectional shapethat is substantially identical with that of the corresponding firstpassage 62 b. When the housing and the fluid-pressurizing members areassembled, a portion of each second end 63 b is placed in thecorresponding guide groove 62 a, and another portion thereof is insertedinto and received in the corresponding first passage 62 b. That is, uponrotation of the rotational shaft 61, the second end 63 b of each of thefluid-pressurizing members 63 is rotated in the first passage 62 b whilebeing guided by the guide groove 62 a. The groove or head receiver incombination with the fluid-pressurizing member or head defines a secondspace (for example, 65 in FIG. 3) having a second volume, which isvariable depending upon the position of the head relative to the housingor plug, the second space being in fluid communication with the firstspace. Further, the first passage 62 b and the second end 63 b of thefluid-pressurizing member 63, which correspond to each other, have thesubstantially same shape in cross section and can be slid relative toeach other in a contact state, so that if the fluid-pressurizing member63 is moved in the first passage 62 b, the working fluid in thefluid-receiving space 72 can be prevented from leaking into the firstand second passages 62 b and 62 g. Although not shown, a sealing membermay be further installed to prevent the working fluid from leakingthrough a clearance between the corresponding second end 63 b of thefluid-pressurizing member 63 and the first passage 62 b, if necessary.

According to this embodiment, the plurality of fluid-pressurizingmembers 63 are simultaneously rotated, so that the moving distance ofthe pressing piston can be increased with a small number of revolutionsof the motor. Consequentially, the responsiveness of the brake actuatingapparatus can be improved. In addition, since the fluid-pressurizingmembers 63 are adapted to be fixed to the fixing disk 66, the brakeactuating apparatus can be easily manufactured. Referring to FIGS. 18A,18B and 18C, the fluid-pressurizing member 63 received in the guidegroove 62 a, in which the fluid-pressuring member 63 is movable betweena first position shown in FIG. 18A and a second position shown in FIG.18B. The fluid-pressurizing member 63 rotates in a first rotationaldirection, stops at a third position shown in FIG. 18C and rotates in asecond rotational direction which is opposite to the first rotationaldirection. As shown in FIGS. 18A, 18B and 18C, the third position islocated between the first position and the second position.

Referring to FIG. 3, in the braking actuating apparatus of thisembodiment, the caliper body 80 is formed with a through-hole 81communicating with an oil-supplying hole 62 c. The brake actuatingapparatus further comprises an oil-supplying tank 95 that is installedon the caliper body 80 and provided with an oil-supplying portcommunicating with the through-hole 81 and has the working fluidcontained therein. The oil-supplying tank 95 is provided with a cap usedfor replenishing the oil-supplying tank with the working fluid andpreventing the working fluid from leaking to the outside. Referring toFIGS. 4 and 5, the oil-supplying hole 62 c for use in replenishing thehousing with the working fluid is formed in at least one of the guidegrooves 62 a of the housing 62. In this embodiment, the oil-supplyinghole 62 c is formed at a position to meet the following requirements.When the fluid-pressurizing member 63 received in the guide groove 62 ais completely inserted into the first passage 62, the oil-supplying hole62 c should not be closed by a side surface of the second end 63 b ofthe fluid-pressurizing member 63 so that the oil can be supplied fromthe outside to the fluid-receiving space 72. When the fluid-pressurizingmember 63 is rotated and enters the fluid-receiving space 72 to performbraking, the oil-supplying hole should be closed by the side surface ofthe second end 63 b of the fluid-pressurizing member 63 so that theworking fluid received in the fluid-receiving space 72 cannot leak tothe outside. The relationship between the position of the oil-supplyinghole 62 c and the positions of the guide grooves 62 a and the firstpassages 62 b is specifically shown in FIG. 5. FIGS. 6 (a) and (b) aresectional views of the housing 62 taken along line A-A and line B-B inFIG. 5, and show that the oil-supplying hole 62 c is formed in an outersurface of the guide groove 62 a, a groove 62 f for receiving an O-ringis formed in a shaft supporting hole 62 d, and a groove 62 e forreceiving an O-ring is formed in an outer periphery of the housing.These figures also show that the second passage 62 g communicates withthe first passage 62 b.

Since the operation principle of the brake actuating apparatus of thisembodiment is the same as an embodiment shown in FIG. 1, a detaileddescription thereof will be omitted.

FIG. 7 is a perspective view of another embodiment of the housing andthe fluid-pressurizing member in the brake actuating apparatus accordingto an embodiment of the present invention, with the housing and thefluid-pressurizing member separated from each other; and FIGS. 8 (a) and(b) are sectional views of the housing taken along line C-C and line D-Din FIG. 73 respectively.

The housing 62 and the fluid-pressurizing members 63 in this embodimentare different from the housing 62 and the fluid-pressurizing members 63shown in FIG. 4 in that the fixing disk 66 is fixed to the rotationalshaft 61 such that the fixing disk 66 faces a surface of the housing 62which is opposite to the surface thereof directed toward the pressingpiston 70, the plurality of fluid-pressurizing members 63 are fixed tothe fixing disk 66, and the second ends 63 b of the fluid-pressurizingmembers 63 are inserted into the second passages 62 g and then receivedin the first passages 62 b.

FIG. 9 is a perspective view of another embodiment of the housing andthe fluid-pressurizing member shown in FIG. 2, with the housing and thefluid-pressurizing member separated from each other. The housing and thefluid-pressurizing member shown in FIG. 9 is different from the housingand the fluid-pressurizing member shown in FIG. 2 in that the second end63 b of the fluid-pressurizing member 63 takes the shape of a circle incross section and the housing is divided into a first disk 62-1 and asecond disk 62-2 for the purpose of easiness of machining, and in thatthe first passage 62 b also takes the shape of a circle in cross sectionin the same manner as the second end 63 b of the fluid-pressurizingmember 63 and a groove 62 h for installing an O-ring is formed toprevent the working fluid from leaking. For the easiness of machining,the first disk 62-1 and the second disk 62-2 are divided by a planepassing through the center of the first passage 62 b.

FIG. 10 is a perspective view of another embodiment of the housing andthe fluid-pressurizing member shown in FIG. 7, with the housing and thefluid-pressurizing member separated from each other. The housing and thefluid-pressurizing members shown in FIG. 10 are different from thehousing and the fluid-pressurizing members shown in FIG. 7 in that thesecond end 63 b of each of the fluid-pressurizing members 63 takes theshape of a circle in cross section and the housing 62 is divided into afirst disk 62-1 and a second disk 62-2 for the purpose of easiness ofmachining, and in that each of the first passages 62 b also takes theshape of a circle in cross section in the same manner as the second end63 b of the fluid-pressurizing member 63 and a groove 62 h forinstalling an O-ring or sealing ring is formed to prevent the workingfluid from leaking. For the easiness of machining, the first disk 62-1and the second disk 62-2 are divided by a plane passing through thecenters of the respective first passages 62 b.

FIG. 11 is a perspective view of a further embodiment of the housing andthe fluid-pressurizing member in the brake actuating apparatus accordingto an embodiment of the present invention, with the housing and thefluid-pressurizing member separated from each other; and FIG. 12 is aperspective view of a still further embodiment of the housing and thefluid-pressurizing member in an electric braking apparatus according toan embodiment the present invention, with the housing and thefluid-pressurizing member separated from each other.

The brake actuating apparatus of this embodiment is different from thebrake actuating apparatus shown in FIG. 3 in that a lever 98 isinstalled at the second gear 52 to rotate the rotational shaft 61 onlyin a direction in which the fluid-pressurizing members 63 enter thefluid-receiving space 72, and in that the housing 62 is divided into thefirst disk 62-1 and the second disk 62-2 and the fluid-pressurizingmembers 63 are provided between the first and second disks.

Referring to FIG. 11, the lever 98 is installed in a gearbox 53 of thepower transmission means 50 by means of a lever shaft 97. A driven wheel95 is fixed to the second gear 52 to mechanically rotate the rotationalshaft 61, and a driving wheel 96 is fixed to the lever shaft 97 to beengaged with the driven wheel 95, thereby rotating the driven wheel 95only in one direction. A driven groove 95 a with a predeterminedcircumferential width and depth is formed in a surface of the drivenwheel 95, which is directed toward the driving wheel 96, and a drivingprotrusion 96 a to be inserted into the driven groove is formed in asurface of the driving wheel 96, which is directed toward the drivenwheel 95. The driven groove 95 a is formed to have a predetermined angleof circumference (a rotating angle of the rotational shaft), and thedriving protrusion 96 a is inserted into the driven groove 96 a at aposition where the rotational shaft 61 can be rotated only in onedirection. Accordingly, if the motor is out of order or an electricaltrouble occurs, the lever 98 can be pulled and rotated so as to rotatethe rotational shaft 61, thereby performing mechanical braking withoutusing the motor. Since the technical constitution for advancing thepressing piston by mechanically rotating the lever as described above isapparent to those skilled in the art, a detailed description thereofwill be omitted. If a device capable of performing mechanical braking isadded to the brake actuating apparatus, the device can be usefullyutilized in an emergency or upon parking of a vehicle.

Referring to FIG. 12, the housing 62 in this embodiment is divided intothe first disk 62-1 disposed at a front side directed toward thepressing piston 70 and the second disk 62-2 disposed at the rear of thefirst disk 62-1.

The guide grooves 62 a and the first passages 62 b are formed in thefirst disk 62-1, and the second passages 62 g communicating with thefirst passages 62 b are formed in the second disk 62-2. Further, someparts of a radially outer wall of the first disk 62-1 at which the guidegrooves 62 a will be formed, and some parts of a surface of the firstdisk 62-1 which is directed toward the second disk and at which thefirst passages 62 b will be formed are removed so that the guide grooves62 a and the first passages 62 b are defined by the inner periphery ofthe cylinder 85 to which the first disk 62-1 is fixed and a frontsurface of the second disk 62-2 which is coupled to the first disk 62-1.The fluid-pressurizing members 63 are installed between the first disk62-1 and the second disk 62-2. The first end 63 a of each of thefluid-pressurizing members is fixed to the rotational shaft 61, and thesecond end 63 b thereof is formed as a stepped axial projection having acircular arc shape so that it can be inserted into the first passage 62b and enter the guide groove 62. An outer surface of the steppedprojection 63 b is in close contact with the inner periphery of thecylinder 85.

FIG. 13 is a schematic view of a brake actuating apparatus according toa further embodiment of the present invention; FIG. 14 is a perspectiveview of an embodiment of a housing and fluid-pressurizing members of thebrake actuating apparatus shown in FIG. 13, with the housing and thefluid-pressurizing members separated from each other; and FIG. 15 is asectional view taken along line E-E in FIG. 14, showing a state wherethe housing and the fluid-pressurizing members are assembled.

The housing and the fluid-pressurizing members of the brake actuatingapparatus of this embodiment are different from the housing and thefluid-pressurizing members shown in FIG. 12 in that the housing 62comprises the hollow first disk 62-1 provided with a large diameterportion 62-1 d and a small diameter portion 62-1 c, thefluid-pressurizing members 63 to be inserted into the small diameterportion 62-1 c, and the second disk 62-2 to be inserted into the largerdiameter portion 62-1 d. Contrary to an embodiment shown in FIG. 12, aradially inner wall of the small diameter portion of the first disk 62-1at which the guide grooves 62 a and the first passages 62 g will beformed, and a surface of the first disk 61-1 which is directed towardthe second disk 62-2 are removed so that the guide grooves 62 a and thefirst passages 62 g are defined by a radially outer surface of the smalldiameter portion 62-1 c, the fluid-pressurizing members 63 inserted intothe small diameter portion 62-1 c and the second disk 62-2 inserted intothe large diameter portion 62-1 d.

In an embodiment shown in FIG. 14, for the purpose of easiness ofmanufacture, circumferential for defining the first passages are removedin the small diameter portion 62-1 c, and an additional sidewall ring62-3 is provided in place of the removed sidewalls. That is, the firstdisk 62-1 is provided with the hollow large diameter portion 62-1 d andsmall diameter portion 62-1 c, and an end of the small diameter portion62-1 c protruding toward the pressing piston 70 is closed. Fourthrough-holes 62-1 a are equiangularly formed in a side surface of thesmall diameter portion 62-1 c, which faces the inner periphery of thecylinder. The sidewall ring 62-3 to be inserted into the small diameterportion 62-1 c takes the shape of a ring with a predetermined width andis provided with through-holes 62-3 a at positions corresponding to thethrough-holes 62-1 a formed in the small diameter portion 62-1 c. On aninner periphery of the sidewall ring 62-3, four sidewalls 62-3 b areformed at circumferential ends of the through-holes 62-3 a. Moreover,the fluid-pressurizing members 63 are inserted into and placed insidethe sidewall ring 62-3. In this embodiment, the fluid-pressurizingmembers 63 are similar to a structure in which a spline is formed on anouter periphery of a disk with the same diameter as the inner peripheryof the sidewall ring 62-3, i.e., the fluid-pressurizing members 63 takea shape obtained by circumferentially removing some parts of the outerperiphery of the disk at a predetermined interval by an amountcorresponding to the height of the sidewalls 62-3 b. That is,protrusions of the spline correspond to the second ends 63 b of thefluid-pressurizing members 63 and the other portion of the splinecorresponds to the first ends 63 a of the fluid-pressurizing membersfixed to the rotational shaft. The second disk 62-2 is equiangularlyformed with four second passages 62 g and is inserted into the largediameter portion 62-1 d of the first disk 62-1.

Referring to FIG. 15, it can be understood that the guide grooves, thefirst passages and the second passages are defined using the housing andthe fluid-pressurizing members of this embodiment in the same manner asthe aforementioned embodiments. That is, region Q denoted by a dottedline and including the through-hole 62-1 a of the small diameter portion62-1 c and the through-hole 62-3 a of the sidewall ring 62-3 defines theguide groove 62 a, and region P denoted by a dotted line among an areain which the second end 63 b of each of the fluid-pressurizing members63 is moved defines the first passage 62 b.

Although the brake actuating apparatus according to various embodimentsof the present invention have been described on the assumption that allof them are used in a caliper brake for a vehicle, the brake actuatingapparatus according to embodiments of the present invention is notlimited thereto but can be used as an actuating apparatus for a varietyof brake systems.

According to an embodiment of the present invention, there is provided abrake actuating apparatus that uses both an electric motor and a fluidand converts a rotational motion from the motor into a force forpressurizing the fluid, thereby performing a braking function, without ameans for converting the rotational motion from the motor into a linearmotion. Accordingly, there is provided a novel braking actuatingapparatus, wherein an additional means for converting a rotationalmotion into a linear motion is not required and thus its structure issimplified and production costs can be reduced. Further, a pressingpiston of the brake actuating apparatus can be urged with a smallrotational force of the motor according to the Pascal's theory regardinga fluid, resulting in decrease in the size of the motor.

When the brake actuating apparatus according to an embodiment of thepresent invention is used in a vehicle, it is possible to eliminate ahydraulic circuit for braking, thereby decreasing the weight of thevehicle and reducing manufacturing costs.

Moreover, the brake actuating apparatus according to an embodiment ofthe present invention is provided with a mean for mechanicallyperforming braking. Thus, even if the electric motor is out of order,the brake actuating apparatus can perform braking, thereby improving thesafety of a brake system.

It is intended that the embodiments of the present invention describedabove and illustrated in the drawings should not be construed aslimiting the technical spirit of the present invention. The scope of thepresent invention is defined only by the appended claims. Those skilledin the art can make various changes and modifications thereto withoutdeparting from the spirit. Therefore, various changes and modificationsobvious to those skilled in the art will fall within the scope of thepresent invention.

What is claimed is:
 1. A brake actuating apparatus, comprising: acaliper body comprising a cylinder, which comprises at least onefluid-contacting surface, a first end and a second end; a piston movablyengaged with the cylinder at the first end, the piston comprising atleast one fluid-contacting surface; a shaft rotatable about an axis; aplug comprising a body fixed to the cylinder at the second end, the plugcomprising at least one fluid-contacting surface; a head connected tothe shaft at a distance from the axis, the head being at least partiallyrotatable about the axis relative to the plug as the shaft rotates aboutthe axis, the head comprising at least one fluid-contacting surface; ahead receiver being a configuration formed in the body of the plug andcomprising at least one fluid-contacting surface, which is other thanthe at least one fluid-contacting surface of the plug, the head receiverbeing configured to receive and liquid tightly engaged with at leastpart of the head, and further configured to guide rotational movement ofthe head relative to the plug; brake fluid filled in a space defined bythe at least one fluid-contacting surface of the cylinder, the at leastone fluid-contacting surface of the piston, the at least onefluid-contacting surface of the plug, the at least one fluid-contactingsurface of the head receiver, and the at least one fluid-contactingsurface of the head; wherein at least partial rotation of the head aboutthe axis relative to the plug is to cause a change in a shape of thespace while substantially maintaining a volume of the space, whichfurther causes a linear movement of the piston along the axis relativeto the cylinder, wherein at least partial rotation of the head about theaxis in a first rotational direction relative to the plug involves atleast partial rotation of the at least one fluid-contacting surface ofthe head about the axis in the first rotational direction, wherein theat least partial rotation of the head does not involve linear movementof the head along the axis relative to the plug.
 2. The apparatus ofclaim 1, wherein the configuration formed in the body of the plugcomprises a groove.
 3. The apparatus of claim 2, wherein at least partof the head is slidably engaged within the groove.
 4. The apparatus ofclaim 2, wherein the groove has an opening facing the piston.
 5. Theapparatus of claim 2, wherein the configuration formed in the body ofthe plug further comprises a hole extending circumferentially about theaxis from the groove, and wherein the head comprises a portion engagedwith the hole and slidable relative to the hole.
 6. The apparatus ofclaim 5, wherein the portion engaged with the hole has a cross-sectionalshape selected from the group consisting of circle, oval and polygon. 7.The apparatus of claim 5, further comprising a sealing ring surroundingthe portion engaged with the hole.
 8. The apparatus of claim 2, whereinthe head receiver comprises one or more additional grooves, wherein thegroove and the one or more additional grooves are disposed in the plugwith the substantially same angular interval between two immediatelyneighboring grooves.
 9. The apparatus of claim 1, further comprising aconnector connecting between the shaft and the head.
 10. The apparatusof claim 9, wherein at least part of the connector is located within thespace.
 11. The apparatus of claim 9, wherein at least part of theconnector is located between the plug and the piston.
 12. The apparatusof claim 1, wherein at least part of the plug is located between thehead and the piston.
 13. The apparatus of claim 1, wherein the plugcomprises a first circular disk having a first radius and a secondcircular disk having a second radius, wherein the first and secondcircular disks are integrated with each other, wherein the firstcircular disk faces the space, and wherein the first radius is smallerthan the second radius.
 14. The apparatus of claim 1, wherein the plugcomprises a through hole extending along the axis and the shaft passesthrough the through hole.
 15. The apparatus of claim 1, furthercomprising an electric motor attached to the caliper body and configuredto rotate the shaft.
 16. The apparatus of claim 1, wherein the head ismovable between a first position and a second position, wherein the headis configured to rotate in the first rotational direction, stop at athird position and rotate in a second rotational direction which isopposite to the first rotational direction, and wherein the thirdposition is located between the first position and the second position.17. An automobile comprising: the apparatus of claim 1; and a brake padattached to at least one of the piston and the caliper body.
 18. Amethod of actuating a brake, the method comprising: providing theapparatus of claim 1; rotating the shaft in a first direction so as torotate the head about the axis and to move relative to the plug, whichcauses a change in the shape of the space while substantiallymaintaining the volume of the space, thereby causing a linear movementof the piston along the axis away from the plug.
 19. The method of claim18, further comprising rotating the shaft in a second direction oppositeto the first direction so as to rotate the head about the axis and moverelative to the plug, which causes a change in the shape of the spacewhile substantially maintaining the volume of the space, thereby causinga linear movement of the piston along the axis toward the plug.
 20. Theapparatus of claim 1, wherein the head does not comprise a mechanism forconverting the at least partial rotation to linear movement thereof.